(1) Field of the Invention
The present invention relates to a connecting rod bearing for an internal combustion engine that is configured so that lubrication oil supplied to an inner circumferential surface of a main bearing supporting a crankshaft is supplied to an inner circumferential surface of a connecting rod bearing supporting a crankpin through an internal lubrication oil path of the crankshaft.
(2) Description of Related Art
A crankshaft of an internal combustion engine is supported at a journal section thereof in a cylinder block lower portion of the internal combustion engine via a main bearing constituted by a pair of half bearings. For the main bearing, lubrication oil which is discharged by an oil pump through a through-hole formed in a wall of the main bearing from an oil gallery formed in a cylinder block wall is fed into a lubrication oil groove formed along an inner circumferential surface of the main bearing. Further, a first lubrication oil path is formed to penetrate the journal section in a diameter direction thereof, so that both end openings of the first lubrication oil path communicate with the lubrication oil groove of the main bearing. Further, a second lubrication oil path passing through a crank arm section is formed to branch from the first lubrication oil path of the journal section, and the second lubrication oil path communicates with a third lubrication oil path formed to penetrate a crankpin in a diameter direction thereof. The lubrication oil fed into the lubrication oil groove formed in the inner circumferential surface of the main bearing through the through-hole from the oil gallery in the cylinder block wall in this manner passes through the first lubrication oil path, the second lubrication oil path and the third lubrication oil path, and is supplied from a discharge port opened at a tail end of the third lubrication oil path to a gap between sliding surfaces of the crankpin and the connecting rod bearing (for example, see JP-A-08-277831).
The lubrication oil fed to the connecting rod bearing through the journal section of the crankshaft from the cylinder block of the internal combustion engine is likely to be accompanied by foreign matters existing in the lubrication oil paths of respective sections. The foreign matters may damage the sliding surface of the connecting rod bearing, if the foreign matters accompany the lubrication oil and are fed to the gap between the sliding surfaces of the crankpin and the connecting rod bearing. Accordingly, the foreign matters entering the gap between the sliding surfaces of the crankpin and the connecting rod bearing need to be quickly discharged to an outside from a sliding surface portion.
Conventionally, as a main bearing and a connecting rod bearing, sliding bearings each composed of a pair of half bearings have been adopted. In the sliding bearing, so-called crush reliefs are formed adjacently to contact surfaces of the half bearings.
A crush relief is a wall thickness-reduced region, which is formed so that a wall thickness of a region adjacent to a circumferential end surface of the half bearing decreases toward the circumferential end surface. The crush reliefs are formed with the objective of absorbing positional displacement and deformation of butting surfaces of the half bearings when the pair of half bearings are assembled (for example, see JP-A-04-219521).
Meanwhile, in recent years, in response to miniaturization of the oil pump for supplying lubrication oil, a bearing has been proposed, in which circumferential grooves are formed on inner circumferential surfaces of circumferential end portions of the bearing by boring, in order to decrease the amount of leakage of the lubrication oil from a bearing end portion (for example, see JP-A-2002-188624).
Furthermore, as a measure dealing with the foreign matters mixed into the lubrication oil, there is the proposal to provide a lubrication oil groove in a circumferential direction throughout the entire length of an inner circumferential surface of a semicircular bearing of the main bearing composed of a pair of half bearings, which semicircular bearing has a through-hole directly receiving supply of the lubrication oil from an oil gallery in a cylinder block wall, and to form gaps in circumferential end portions of the inner circumferential surface, whereby the foreign matters accompanying the lubrication oil and entering the lubrication oil groove are discharged so as to be dispersed into the plurality of circumferential grooves in the circumferential end portions of the inner circumferential surface of the semi-cylindrical bearing, and further are discharged to an outside of the bearing through an axial groove formed on inner circumferential surfaces of butting portions of the circumferential end surfaces of a pair of semi-cylindrical bearings (for example, see JP-A-2011-58568).
It was confirmed that when the above idea is applied to a connecting rod bearing, the effect of discharging the foreign matters cannot be obtained, and in addition, the foreign matters remain in the circumferential lubrication oil groove formed throughout the entire length of the inner circumferential surface of one of the half bearings for the connecting rod. Further, it was also confirmed by a test that the foreign matters are dispersed throughout the entire bearing sliding surfaces, so that damage to the bearing easily occurs, and therefore, the idea has the opposite effect to what was expected.
This is because in general, a housing holding a connecting rod bearing deforms significantly during operation of an internal combustion engine, and a gap between a crankpin section and a connecting rod bearing is larger than a gap between a journal section and a main bearing, as a result of which, the foreign matters held in the lubrication oil groove easily spread to the entire bearing sliding surfaces, the foreign matters are also distributed to the sliding surface portions in the “circumferential central portion of a half bearing” which is a main load portion, and the bearing damage increases more than the case of using the connecting rod bearing of the conventional type which is not provided with a circumferential lubrication oil groove.